Both Ni(II) andCr(VI) are known carcinogens and the damage to DNA caused by these metal ions results from redox reactions. Metallothionein (MT) is a ubiquitous, low molecular weight, cysteine-rich protein that binds both essential and toxic metal ions and appears to play a key role in metal metabolism. The overall objective of this project is to determine the role that MT plays in the carcinogenesis of Ni(II) and Cr(VI). While both metal ions cause similar oxidative damage to DNA, we propose that MT participates differently in the redox reactions of Ni(II) and Cr(VI) in vivo, with indirect interaction in the case of NI but direct interaction in the case of Cr. Metallothionein and Nickel Carcinogenesis: Ni(II) induces the biosynthesis of MT which removes Zn(II) from zinc finger transcription factors, allowing NI(II) to bind to these factors resulting in altered gene expression and the generation oxygen radicals which damage DNA. Determine if Ni(II)-transcription factor complexes form under competitive binding conditions with apo-MT and Zn(II). Determine if redox reactions of Ni(II)-transcription factor complexes generate reactive oxygen species and damage protein and DNA in vitro. Determine if MT affects Ni-induced cellular toxicity and the extent and type of DNA damage by Ni(II) by studying CHO cell lines expressing different levels of MT. Determine whether MT plays a role in Ni(II) effects on specific gene expression of genes regulated by Sp1 and the glucocorticoid receptor. Metallothionein and chromium Carcinogenesis: redox reactions of Cr(VI) and Zn7MT under different pH conditions. Determine if Cr(V) complexes or oxygen radicals produced in the reaction of CrO4-2 with Zn7MT damage DNA in vitro. Determine if MT affects Cr-induced cellular toxicity and DNA damage by Cr(VI) by studying CHO cells expressing different levels of MT. Determine whether MT plays a role in Cr(VI) effects on expression of genes regulated by Sp1 and the glucocorticoid receptor.